Strength Of Lightweight Aggregate Concrete Research Articles

Impact of fine lightweight aggregates and coal waste on structural lightweight concrete: Experimental study and gene expression programming

Light Expanded Clay Aggregate (LECA) is one of the materials used to make lightweight concrete. In this study, two types of lightweight aggregates including LECA in both coarse and fine aggregate forms and pumice in fine aggregate form have been used to produce lightweight aggregate concrete. Coal waste is also used as partial replacement for cement. The results show that the usage of pumice as partial replacement for sand and LECA as coarse aggregate is applicable and can used for producing structural lightweight aggregate concrete. Furthermore, by using and increasing in the amount of LECA as fine aggregate, the slump of lightweight concrete in comparison to using sand, is also increased. The mixtures with LECA in both fine and coarse aggregate forms have the best results. Also, the results show that adding the coal waste improves the properties of lightweight concrete, and the optimal ratio is about 15% as partial replacement for cement by weight. In addition, gene expression programming is employed to establish empirical connections derived from experimental outcomes. In this regard, a relationship is proposed to determine the compressive strength of lightweight aggregate concrete based on the experimental data. The outcomes of gene expression programming demonstrate that the suggested formula exhibits good accuracy and efficiency in forecasting the specified parameter.

A novel foaming-sintering technique for developing eco-friendly lightweight aggregates for high strength lightweight aggregate concrete

To address the scarcity of natural aggregates and reduce energy consumption in the concrete industry, a sustainable lightweight aggregate (LWA) was prepared with a self-foaming and sintering method by utilizing waste glass powder as the primary precursor and incineration bottom ash as a foaming agent. The effect of NaOH content (0 M, 2 M, and 8 M) on the physical properties of LWA was investigated. Replacing manufactured sand with sintered LWA (0 M-LWA and 2 M-LWA) by 50 vol% and 100 vol% to investigate their impact on the physical properties, mechanical properties, shrinkage, and alkali-silica reaction of high strength LWA concrete. The high strength LWA concrete prepared with 0 M-LWA possessed a density of 2127 kg/m3 and compressive strength of 108.7 MPa, which were slightly lower than that with manufactured sand. Due to the porous and lightweight nature of 2 M-LWA, the density and compressive strength of LWA concrete significantly decreased with the increased 2 M-LWA volume. Nevertheless, 100%-2M showed satisfying density of 1835 kg/m3 and compressive strength of 50 MPa. The internal curing effect of 2 M-LWA effectively mitigated the autogenous shrinkage of LWA concrete. The alkali-silica reaction expansion of all LWA was innocuous.

Experimental and theoretical analysis of FRP-confined square lightweight aggregate concrete columns under axial compression

The structure of an FRP-confined square lightweight aggregate concrete (LWAC) column was investigated, and it was found to significantly decrease the self-weight while improving the deformation capacity and bearing capacity. Twelve FRP-confined LWAC columns and three unconfined LWAC columns underwent monotonic axial compression tests. The influences of the FRP thickness and type on the compressive performance, stressstrain relationship and strain cloud maps were investigated based on digital image correlation (DIC) technology. Both types of FRP materials demonstrated a noticeable enhancement in both the strength and deformation capacity of LWAC, with CFRP having the greatest effect on strength and BFRP having the greatest effect on ductility. Compared to LWAC columns without confinement, the compressive strength of LWAC confined by BFRP or CFRP increased by 9.4∼21.9% and 24.9∼53.3%, respectively, and the ultimate strain increased by 10.6–14.2 times and 8.0–10.9 times, respectively, with increasing the thickness of FRP. DIC technology was used to accurately measure changes in the strain and the crack development of the specimens, thereby obtaining an accurate rupture strain of the FRP material. The existing models were evaluated using test data, and new models were proposed for FRP-confined square LWAC.

Applying Microbial-Induced Calcium Carbonate Precipitation Technology to Improve the Bond Strength of Lightweight Aggregate Concrete after High-Temperature Damage

High temperatures and external force can easily lead to a decline in the bond strength of reinforced concrete components. Microbial-induced calcium carbonate precipitation (MICP) technology has considerable potential for repairing concrete. Given this, this study utilized MICP technology to improve the bond strength of heat- and pull-damaged lightweight aggregate concrete (LWAC). The specimens of a control group (Group A) and two experimental groups (Group B and Group C) were prepared. The experimental group was prepared using lightweight aggregates (LWAs) that had been immersed in a nutrient solution and a bacterial solution. The control group was prepared using LWAs that were not immersed in a nutrient solution or bacterial solution. These specimens healed themselves in different ways after exposure to high temperatures (300 °C and 500 °C) and pull-out damage. Groups A and B adopted the same self-healing method; that is, their specimens were placed in a computer-controlled incubator at 40 °C. Group C used different self-healing methods. The specimens in this group were soaked in a mixed solution of urea and calcium acetate at 40 °C for two days and then taken out and placed in an incubator at 40 °C for two days. A cycle took four days until the expected self-healing age was reached. After being exposed to 300 °C and self-healed for 90 days, the residual bond strengths of the secondary pull-out tests in Groups A, B, and C were 20.63, 22.13, and 25.69 MPa, respectively. Moreover, compared with Group A, the relative bond strength ratios of the secondary pull-out tests in Groups B and C increased by 5.8% and 20.3%, respectively. This demonstrates that MICP technology could effectively improve the bond strength of LWAC after high-temperature and pull-out damage.

Experimental evaluation of fracture toughness of basalt macro fiber reinforced high performance lightweight aggregate concrete

High performance lightweight aggregate concrete has become a popular topic for the development of green concrete due to the incorporation of various industrial wastes to substitute aggregate. However, its brittleness has gradually emerged as an issue with the increasing of compressive strength. To address this concern, the authors in this paper investigated the influence of basalt macro fiber (BMF) on the compressive and splitting tensile strengths of lightweight aggregate concrete at different fiber volume contents and lengths. Moreover, the three-point bending test on notched beams, with the help of acoustic emission and digital image correlation, was also carried out to evaluate the fracture toughness of basalt macro fiber reinforced lightweight aggregate concrete. Finally, the softening constitutive model was determined in the present study. The results showed that the addition of BMF increased the compressive strength of lightweight aggregate concrete and the maximum increase reached 9.03%. As for splitting tensile strength, the maximum increase was 39.88%. In addition, it was observed that the incorporation of basalt macro fiber significantly improved the initial cracking toughness and unstable fracture toughness of plain specimen. The fracture energy of BMF reinforced lightweight aggregate concrete was also increased, and the largest improvement was seen in BMF-0.5–22.5 group, 8.5 times that of plain specimen.

Shrinkage prediction model of high strength lightweight aggregate concrete based on relative humidity

Concrete shrinkage affects the overall stability and long-term service performance of the structures. Lightweight aggregates (LWAs) with a porous structure are an ideal internal curing material to mitigate concrete shrinkage. Nevertheless, the low elastic modulus of LWAs has a negative impact on concrete shrinkage. In order to clarify the influences of LWAs in the high strength lightweight aggregate concrete (HSLC) on its shrinkage performance, the compressive strength, internal relative humidity (IRH), elastic modulus, and autogenous shrinkage (AS) of HSLC were analyzed experimentally in this study. The correlation of these parameters was investigated. As indicated by the results, compressive strength and elastic modulus were negatively related to the content of LWAs. The 28-day AS and IRH of HSLC and the critical moment of IRH increased by 3.9%, 20.2% and 36 h, respectively, when the content of LWAs increased from 0% to 100%. A linear relationship between AS and compressive strength and an exponential relationship between AS and IRH were established. Additionally, a shrinkage prediction model considering IRH of concrete and water absorption by LWAs was proposed for HSLC.

Compressive and flexural toughness indices of lightweight aggregate concrete reinforced with micro-steel fibers

There remains a lack of comprehensive investigations examining ductility of the fiber-reinforced lightweight aggregate concrete (LWAC) elements, necessitating a deeper exploration. The purpose of this study is to assess the effect of micro-steel fibers on the compressive and flexural toughness capacities of LWAC. A total of twenty-one LWAC mixtures were prepared, varying the test parameters of the compressive strength of concrete and fiber volume fraction. The toughness capacities of fiber-reinforced LWAC were calculated using the stress–strain curves in compression and flexural load–deflection curves measured for each specimen, in accordance with ASTM C1018. These were compared with those of the previous normal-weight concrete and LWAC specimens reinforced by single macro-steel fibers or a combination of macro-steel fibers and micro synthetic fibers. The effect of numerous fiber parameters on the toughness of concrete was considered as a function of the fiber reinforcing index. Simple closed-form equations from the literature were modified to reliably determine the compressive and flexural toughness indices of micro-steel fiber-reinforced LWAC. Additionally, the relationship between equivalent flexural strength ratio and flexural toughness indices was formulated from a regression analysis using test datasets. Test results showed that the addition of only 0.25% micro-steel fibers significantly enhanced strength and toughness in compression and flexure. Moreover, better dispersion of steel microfibers enabled greater LWAC strength and toughness increases through a denser restriction of crack propagation.

Effect of Graphene Oxide on compressive strength of Shale Ceramsite high strength lightweight aggregate concrete

The use of shale ceramsite to produce high-strength lightweight concrete (HSLWC) in the construction industry is an effective method for sustainable development and environmental protection. The growing demand for HSLWC has stimulated the development of nanomaterials to further enhance mechanical properties. This study investigated the effect of graphene oxide (GO) on the properties of HSLWC with shale ceramsite as a coarse and fine aggregate, including workability, density, compressive strength, and energy dispersive spectrometer (EDS) test. The control mixture was designed according to the standard of grade 40 high strength concrete, and four groups of mixtures were prepared by adding doses of GO at 0.00%, 0.02%, 0.04% and 0.06% by weight of cement to the control mixture. The experimental results showed that HSLWC with the 28-day compressive in the range of 43-54 MPa and the oven dry density of 1705-1783 kg/m3 could be produced by using shale ceramsite and shale pottery sand as coarse aggregate and fine aggregate, respectively. Simultaneously, adding a low content of GO to HSLWC could slightly increase the density, rationally reduce the slump, and significantly enhance the compressive strength. The EDS results showed that the reason for the increase in compressive strength was that GO could accelerate the cement hydration process and regulate the crystal morphology of the cement.

A Machine Learning Approach to Prediction of the Compressive Strength of Segregated Lightweight Aggregate Concretes Using Ultrasonic Pulse Velocity

Lightweight aggregate concrete (LWAC) is an increasingly important material for modern construction. However, although it has several advantages compared with conventional concrete, it is susceptible to segregation due to the low density of the incorporated aggregate. The phenomenon of segregation can adversely affect the mechanical properties of LWAC, reducing its compressive strength and its durability. In this work, several machine learning techniques are used to study the influence of the segregation of LWAC on its compressive strength, including the K-nearest neighbours (KNN) algorithm, regression tree-based algorithms such as random forest (RF) and gradient boosting regressors (GBRs), artificial neural networks (ANNs) and support vector regression (SVR). In addition, a weighted average ensemble (WAE) method is proposed that combines RF, SVR and extreme GBR (or XGBoost). A dataset that was recently used for predicting the compressive strength of LWAC is employed in this experimental study. Two different types of lightweight aggregate (LWA), including expanded clay as a coarse aggregate and natural fine limestone aggregate, were mixed to produce LWAC. To quantify the segregation in LWAC, the ultrasonic pulse velocity method was adopted. Numerical experiments were carried out to analyse the behaviour of the obtained models, and a performance improvement was shown compared with the machine learning models reported in previous works. The best performance was obtained with GBR, XGBoost and the proposed weighted ensemble method. In addition, a good choice of weights in the WAE method allowed our approach to outperform all of the other models.

Shrinkage Prediction Model of High Strength Lightweight Aggregate Concrete Based on Relative Humidity

Shrinkage Prediction Model of High Strength Lightweight Aggregate Concrete Based on Relative Humidity

Predicting stress-strain behavior of normal weight and lightweight aggregate concrete exposed to high temperature using LSTM recurrent neural network

Lightweight aggregate is commonly used to reduce the self-weight of concrete elements which can efficiently mitigate the environmental impact. This study investigates the mechanical performance of normal weight aggregate concrete (NWAC) and Lightweight aggregate concrete (LWAC) exposed to high temperature, focusing on developing a predictive model for the stress-strain relationship of the LWAC based on the property of cement, silica fume, light weight aggregate and water/cement ratio. Mechanical properties of 30 different mixtures, including uniaxial compressive stress–strain relationship, compressive strength, modulus of elasticity, and failure strain are determined before and after high temperature exposures at 250, 500, and 750 °C. Results show that the modulus of elasticity and compressive strength of LWAC increased with exposure temperature. In particular, mixture S4 was found to outperform other mixtures, which retained 96, 75, and 46 % of compressive strength following exposures to 250, 500, and 750 °C, respectively. At all the temperatures investigated, the specimens of this mixture were able to achieve satisfactory modulus of elasticity and maximum strain. The specimens prepared with mixtures containing 75 % LECA (S23) showed a higher retention compressive strength at 750 °C. This study also utilizes the long short-term memory (LSTM) neural network to predict the stress-strain relationship of NWAC and LWAC mixtures after exposure to high temperatures. The results show that the LSTM model could adequately predict the stress-strain relationship of both LWAC and NWAC mixtures in terms of compressive strength, modulus of elasticity, and failure strain at elevated temperatures.

Shear Capacity Analysis of Steel Reinforced Lightweight Concrete Elements Based on The Bond Strength

Push-out tests of steel reinforced lightweight concrete(SRLC) were carried out for nine specimens which were designed according to the orthogonal test method considering four influence factors including strength of lightweight aggregate concrete, stirrup ratio, thickness of protective layer and anchorage length. The curves of average bond stress and loading-end slip were drawn, the characteristics of split failure and push-out failure were analyzed, and the characteristic bond strength was obtained. Combined with the test results of other scholars on the ultimate bond strength of steel reinforced concrete(SRC), it is found that the bond strength of SRLC is not worse than that of normal concrete(NC) which can be taken the same as 0.5MPa. Then the obtained bond strength can be used to calculate the shear strength of SRLC elements which may occur two forms of shear failure-diagonal shear failure and shear bond failure, however, shear bond failure is ignored in some specifications. Shear bond failure capacity computational formula of SRLC elements is deduced into which the bond strength is introduced.To verify the reasonability and accuracy of the proposed approach, the shear capacity and failure pattern are predicted by the proposed means with previous test results and are also compared with other provisions. The analyses and calculations indicate that the proposed method can accurately predict the shear failure mode and the calculated shear capacity values are in better agreement with the experimental results.

Effect of Steel Inorganic Fiber on Mechanical Properties of Lightweight Aggregate Concrete

In order to study the influence of steel-inorganic fiber on the mechanical properties of lightweight aggregate concrete, test parameters including single ceramic fiber and basalt fiber with different dosage and mixed steel-basalt fiber and steel-ceramic fiber reinforced lightweight aggregate concrete specimens with different doping methods were designed, and compared with the non-fiber reference group. The test results show that the compressive strength of cube is improved most obviously by steel-basalt fiber, with the maximum increase of 14.5%. Adding 1.35kg/m3 basalt fiber can increase the flexural strength of lightweight aggregate concrete by 62.2%. Adding ceramic fiber reduces the compressive strength of lightweight aggregate concrete, but improves the flexural strength.

Mechanical properties of lightweight expanded clay aggregate (LECA) concrete

The construction activities are based on structural concrete, which is one of the most commonly used materials. The fundamental aim of using lightweight concrete (LWC) was to reduce the concrete self-weight of the structure parts. As a result, LWC has been used successfully in a variety of installations for several years. In this paper, the mechanical properties of concrete made with lightweight expanded clay aggregate (LECA) as a full replacement for coarse aggregate are studied. The experimental program shows that LECA with a 32 MPa cube compressive strength and an 1,823 kg×m–3 dry density can be used to make structural light-weight aggregate concrete (SLWC). The results show that the reduction in the strength of lightweight aggregate concrete (LWAC) was found to be higher in the concrete with an estimated compressive strength of 32 MPa due to the lower strength of the LWA (expanded clay). According to the test results, the mechanical properties of LWC were greatly improved by adding silica fume (SF). Furthermore, LECA concrete has a splitting tensile strength that is 47% higher than the ASTM C330/C330M-17A minimum requirement. The LECA concrete has a splitting tensile strength to compressive strength ratio of approximately 13%. Additionally, the results demonstrate a 27% difference in the modulus of elasticity between the calculated and tested values.

Comparison of lightweight and normal-weight aggregate concrete

In this experimental study, lightweight aggregate concrete (LWAC) and normal-weight aggregate concrete (NWAC) were compared within the contexts of the size of calcium hydroxide (CH) crystals in interfacial transition zone (ITZ), compressive strength, and oven-dry density. Six LWAC and NWAC mixtures were prepared for this study. Thirty-six images obtained from Scanning Electron Microscope (SEM) were used to determine the size of CH crystals in ITZ of LWAC and NWAC. Eighteen test specimens (three for each of the six LWAC and NWAC mixtures) were prepared in 150x300 mm sizes and in the form of cylinders for the compressive strength tests and also eighteen test specimens in 100x100x100 mm sizes and in the form of cubes for the oven-dry density tests. It was determined that the size of CH crystals in ITZ of LWAC is 8.43% less than (on average), compressive strength of LWAC is 39.09% more than (on average), and oven-dry density of LWAC is 10.97% less than (on average) the NWAC’s that has the same volumetric proportions of ingredients. The findings of this study show that lightweight aggregate that has high particle density, angular shape, rough surface texture, and a structure that enables chemical reaction with CH crystals will be beneficial for the ITZ microstructure and properties of concrete. It is considered that these properties should be taken into consideration in the selection of lightweight aggregate for structural concrete production.

Study of the structural-functional lightweight concrete containing novel hollow ceramsite compounded with paraffin

In this paper, a structural-functional lightweight aggregate concrete (LWAC) with novel hollow ceramsite (HC) compounded with paraffine was prepared and studied. The mechanical and thermal properties of LWAC with HC-Paraffin are investigated and multiple thermal cycles are tested to evaluate the stability of this novel energy storage concrete. Results show that, the energy storage density (Des) of HC-paraffin is 85.23 J/g in the temperature range 15 °C–45 °C and the latent heat of HC-paraffin is 51.09 J/g. Compressive strength of LWAC with HC-Paraffin is 41.9 MPa which fully meets the requirements of structural building application. The amount of paraffin (8.1 wt%) introduced by HC is relatively advantageous in the current energy storage concrete researches. Compare to control group, the peak temperature and temperature fluctuation of LWAC panel with HC-Paraffin reduce about 5.2 °C and 7.6 °C respectively during the thermal test. Morever, the LWAC with HC-Paraffin shows good stability of mechanical and thermal property. The compressive strength of concrete increases about 8.6 % and the thermal regulation ability of concrete panel has no obvious degradation after 100 thermal cycles. This research gives a new method for the shape stable PCMs which can be directly used in building envelope, providing an alternative for the application of PCMs in buildings.

Bond-slip behaviors of composite steel-reinforced high strength lightweight aggregate concrete columns with innovative X-shaped steel sections

This paper provides an insight into the bond-slip performance of the new type of steel-reinforced high strength lightweight aggregate concrete (SRLWAC) column with innovative X-shaped steel sections through experimental and theoretical studies. Three SRLWAC specimens were tested under push-out force; the variables are the confinement by stirrups (ρsv) and shear connectors (SCs). Force-slip curves, force axial and horizontal deformations, failure modes, and crack patterns of the specimens were investigated; the force transfer, bond-stress, bond shear transmission length, and strains were studied. Comparisons between the bond strength of the studied specimens and ordinary types column specimens from 13 previous studies showed a superior bond capacity for the new type specimens. Five related models of bond capacity were discussed, and the utility of the models was put forward. A simplified load-slip model was proposed and verified. The most feasible model and the simplified model were used in the parametric study. The results showed that the material strengths and geometric configurations parameters affect the bond strength capacity. The confinement and SCs have effects on the bond and failure mode. The natural bond-stress combined with SCs produced smaller bond strength than that from both natural bonds and using higher ρsv. Recommendations for future works are developed.

Determination of compressive strength of lightweight aggregate concrete in service using gene expression programming based on semi‐direct ultrasonic pulse velocity testing

AbstractStructural lightweight aggregate concrete (SLWAC) can increase the ability of buildings to resist earthquakes by significantly reducing the overall weight of structures. Determining a relationship for assessing the concrete compressive strength of these structures using non‐destructive methods can save both time and money. This study aims to estimate the compressive strength of SLWAC using a model of gene expression programming (GEP) and semi‐direct ultrasonic pulse velocity. A hundred specimens of lightweight concrete were made using clay and natural (mineral) pumice aggregates with the maximum nominal sizes of 12.7 mm (½ inch) and 19.2 mm (¾ inch), respectively. Semi‐direct ultrasonic testing of the specimens was then undertaken in the laboratory. The results show a high correlation coefficient for the equations derived from the GEP. Moreover, the equations obtained from GEP for three types of SLWAC, based on semi‐direct ultrasonic pulse velocity, are compatible with equations obtained from the direct ultrasonic velocity method. The simplicity of generated equations increases the practicality and convenience in the working environment and actual conditions. The R2 (goodness of fit) values of proposed equations for LWA01, LWA02, and LWA03 specimens were 0.912, 0.962, and 0.985, respectively. It was concluded that based on the semi‐direct ultrasonic pulse velocity and derived formulas, the compressive strength of SLWAC can be confidently predicted using GEP.

Compressive Strength of Lightweight Aggregate Concrete Containing Crushed Cockle Shell as Partial Sand Replacement

The widespread use of natural sand mined from the river for concrete production worldwide causes environmental degradation. The cockle shell waste from aquaculture industry which discarded at dumpsite also pollutes the environment. Utilization of cockle shell as partial sand replacement in concrete would reduce the harvesting of sand from the river and limit the waste dumping from cockle industry. The experimental research investigates the effect of different sizes crushed cockle shell (600µm and 2.36mm) as partial sand replacement on the workability and compressive strength of lightweight aggregate concrete. 5 types of concrete mixes consisting various percentages of crushed cockle shell ranging from 0%, 5%, 10%, 15% and 20% were used in this research. All specimens were water cured until the scheduled testing time. The workability and compressive strength of concrete were determined via slump test and compressive strength test respectively. The outcome shows that the use of different sized crushed cockle shell as partial sand replacement influences the workability and strength of concrete. The concrete becomes more workable when larger quantity of crushed cockle shell is used. Integration 5% of 600µm and 10% of 2.36mm crushed cockle shell forms concrete with the targeted strength. Using crushed cockle shell as mixing ingredient in concrete reduces quantity of waste thrown and contributes to cleaner surrounding.

Effect of Spent Garnet Waste as Partial Fine Aggregate Replacement on Properties of High Strength Lightweight Aggregate Concrete

As time goes on, the usage of natural resources for concrete production affects the environment. Both the quarrying activities for granite aggregate harvesting and sand mining destroys the environment. At the same time, industrial by-products namely palm oil clinker (POC) and spent garnet waste which thrown as waste, also cause pollution. The inclusion of spent garnet waste as fine aggregate replacement in POC lightweight aggregate concrete production would reduce the consumption of river sand. This research investigates the effect of using spent garnet waste as a fine aggregate replacement on workability, dry density, and compressive strength of POC lightweight aggregate concrete. Five concrete mixes were prepared by varying the percentage of spent garnet waste as a fine aggregate replacement up to 40% by the weight of fine aggregate. All concrete specimens underwent water curing until the testing age of 7 and 28 days. The specimens were tested to determine dry density and compressive strength. Overall, the use of spent garnet as partial fine aggregate replacement influences the concrete properties. Inclusion of 20% spent garnet in concrete resulted in formation of semi-lightweight concrete with density of 2240 kg/m3. On top of that, the concrete with spent garnet exhibit higher compressive strength of about 60MPa which is about 14% higher than control specimen. Conclusively, the utilization of spent garnet as a partial fine aggregate replacement would save river sand consumption and reduce the dumping of spent garnet.